Antenna efficiency is especially important for satellite communications ground terminals, where signals from distant satellite transponders can be weak. Antennas with poor efficiency may receive less signal power and introduce more noise into the signal than a high efficiency antenna, which for dish type terminals means that a larger dish area may be required, increasing the cost and footprint of the ground terminal. Further, in communications systems that both transmit and receive, interference from the transmit signal may reduce the sensitivity of the communications system to the receive signal or may burn out components of the system such as low noise amplifiers.
To achieve high efficiency, low system noise, and provide isolation between signals, satellite communications systems typically use a horn-type feed antenna with an orthomode transducer (“OMT”). While horn-type feed antennas and OMTs can provide satisfactory performance, specialized OMTs increase the complexity and cost of the feed system. Antennas for satellite communications are also typically fixed, and the antenna beam must be physically adjusted by moving the antenna structure to compensate for errors in positioning. Moreover, horn-type feeds are machined parts that must be attached to a printed circuit board containing other common functions in satellite communications systems, causing the size of the system to be heavy, large in size, and costly to manufacture.